A static pressure orifice is one of the facilities for taking measurements of the forces acting on a model in a wind tunnel test. A typical orifice, of which there are a wide variety of types, ranges from 0.03 to 0.125 of an inch in diameter and is disposed in the surface of the model being tested. Static orifices are generally disposed in a plane parallel to the streamlines of the airflow over the model such that the presence thereof does not disturb the airflow stream lines. Inside the body of the model being tested, a tube leads from the orifice through the body of the model, out of the wind tunnel, to a pressure receiving gauge. When the wind tunnel is in operation, the static pressure acting on the model at the point of the static orifice is transmitted through the connecting tube to the pressure receiving gauge, and may be known by a reading of the gauge. The combination of the orifice, the connecting tube, and the pressure receiving gauge comprises a distinct "static pressure orifice system." Each orifice system functions independently. There may be hundreds of static pressure orifices in a model being wind tunnel tested, and the orifices may be spaced close together.
From the readings of a pressure gauge, or of multiple gauges taken together, are derived data on airflow characteristics, Mach numbers, pressure ratios, etc. The orifice system is one of the primary data acquisition methods in aerospace research.
Occasionally faults occur in an orifice system, such as a leak between the orifice and the connecting tube, or in the tube itself, or the system may become clogged by a solid particle strayed into the wind tunnel, or the pressure receiving gauge may lose its accuracy. If any of these conditions occur, the data obtained from reading the gauge is unreliable and essentially worthless. It is therefore necessary, when the wind tunnel is shut down for routine maintenance, to individually test each of the numerous static pressure orifice systems to ensure its integrity.
The prior art method of testing orifice systems generally requires at least two separate operations: First, orifice system pressure receiving instruments are calibrated by disconnecting the line between the orifice and the pressure receiving gauge or instrumentation. An accurate pressure indication gauge and a pressure regulator are then connected to the line going to the pressure receiving gauge or instrumentation. A calibrated pressure is then applied and the receiving instrumentation interpreted to ensure correlation of the orifice system. On completion of the calibration, the calibrated pressure gauge and pressure regulator are disconnected and the orifice and receiving instrumentation reconnected. Thus, the integrity of the orifice system has been momentarily interrupted. In doing so, the possibility of creating a leak in what was previously a secure and reliable orifice system is greatly increased, especially as there are numerous (often several hundred) connecting tubes in proximity which may be crossed. All that has really been determined is the orifice system pressure receiving instrumentation accuracy, not the total orifice system reliability.
Second, to leak check the total orifice system and ensure that the line is correctly connected and that no blockages have occurred, an additonal check is made at the orifice itself. This is usually done by using a piece of transparent plastic tubing connected to a vacuum pump and/or regulator. The tube must be hand held over the orifice and it is often difficult to acquire a satisfactory seal resulting in a loss of time and questionable check. It is also necessary to close a clamp on the tubing, and to read the vacuum gauge, which requires a second technician.
There is thus a definite need in the art for a more simple, efficient, and reliable means of testing orifice systems for leaks, blockages, and misconnections, and calibrating pressure receiving gauges.
Accordingly, it is an object of the present invention to provide an improved method of verifying that static pressure orifices are connected to their respective gauges.
It is another object of the present invention to provide an improved method of detecting leaks and blockages in a static pressure orifice system.
It is a further object of the present invention to provide an improved method of calibrating the pressure receiving gauges in a static pressure orifice system.
It is also an object of the present invention to provide an improved apparatus for verifying that static pressure orifices are connected to their respective gauges.
It is an additional object of the present invention to provide an improved apparatus for detecting leaks and blockages in a static pressure orifice system.
It is yet another object of the present invention to provide an improved apparatus for calibrating the pressure receiving gauges in a static pressure orifice system.